Anisotropic boron nitride is a form of boron nitride having unequal physical properties along different axes. In a large crystallite of anisotropic boron nitride, all the planes are parallel to each other. Lamination occurs because weak Vander Waals forces acting over long distances allow the planes to slide across each other causing lamination. The difficulty with the laminated boron nitride is its inability to form a strong bond and hold together. This obviates its use in such desireable applications as microwave and millimeter wave devices.
Heretofore, the undesirable laminated anisotropic boron nitride has been prepared in general by reacting a boron halide such as boron trichloride with ammonia according to the reaction: EQU BCl.sub.3 +4NH.sub.3 .fwdarw.BN+3NH.sub.4 Cl
The reaction is non reversible, that is, no equilibrium exists between BN+3NH.sub.4 Cl with BCl.sub.3 +4NH.sub.3. Heat is required in this reaction and the boron nitride is deposited on a hot substrate.